Validation of Thermal Processing Using Time-Temperature Indicators as Process Probes

Thermal processing is a very common technique in the food industry. Commonly foods are overprocessed to ensure safety, but this may give excessive loss of quality attributes. Thermocouples are commonly used to obtain temperature-time profiles, but for many products it is not feasible to use them. Time-temperature indicators (TTIs) are small particles containing a reactive species that can be passed through a process and then assayed to measure the process effects. A series of tests have been carried out to determine the feasibility of using TTIs to validate thermal processes, using a pilot scale process vessel. TTI results could show the effects of local wall heating and distinguish between different heating regimes. Particle paths can be quantified using Positron-Emission Particle Tracking (PEPT); for viscous fluids of the kind found in food applications there is very close match between the flow of the fluid and of the TTI. Suggestions for the use of TTIs are made.